This invention relates to a pressure controller and particularly to such a controller for a vacuum operated flow system.
In flow systems, the pressure differential for establishing flow may include a downstream vacuum source. A temporary storage means such as a storage tank, a standpipe or the like within which liquid is stored until it reaches a selected level may be incorporated into the system. When such a selected level is reached, a discharge apparatus is actuated to remove liquid generally until a lower limit is established.
A particularly satisfactory two-position liquid level controller for a vacuum operated sewage disposal system and the like is disclosed in U.S. Pat. No. 3,777,778. The fluid sensor is mounted upstream of the discharge control valve and is connected to actuate a triggered controller having a fluid relay connected to charge a fluid timing capacitor which, in turn, actuates a fluid switch. The timing capacitor is preferably a storage device connected to atmospheric pressure through an adjustable resistor. When the output signal from the sensor is received, the vacuum connection to the capacitor is momentarily made and the vacuum established as a reference. The capacitor output signals the fluid switch which actuates a pilot valve to open the main valve. The sewerage flow continues until such time as the main capacitor has totally discharged, at which time the switch converts to an "off" condition, resetting the pilot valve and moving the main valve to a closed condition. The timing provides a constant volume of the liquid discharged per cycle independent of the input flow into the system. This is particularly significant in flow systems which rely on a slug or incremental liquid transfer in response to a given condition; such as a vacuum powered sewage transport system and the like.
In certain sewage disposal systems, a relatively high vacuum pressure, significantly higher than that employed in the conventional domestic distribution system, is required to remove the sewage from a storage tank or the like. For example, in a marina the sewage is pumped from boat holding tanks and the like into a large storage tank. At a selected volume or level of sewage the storage tank is emptied into a discharging system. In the transfer system, a vacuum level on the order of twelve to fourteen inches of mercury is generally employed. Although the vacuum sewage systems, such as shown in above identified patent and application, provide a highly satisfactory basic system for a marina and like high pressure system, it is important that pumping does not begin prior to creation of an appropriate vacuum system pressure. Further, the sewage system should operate automatically in the presence of proper pressure conditions.